In recent years, electronic devices have been required to have a low dielectric constant, and accordingly, heat-resistant materials with voids have been required. As a base material for these heat-resistant materials, a heat-resistant non-woven fabric capable of bearing a solder connecting process is one of promising candidates. The heat-resistant non-woven fabric receives attention as a material which exhibits excellent ion permeability and high mechanical strength and thermal resistance when subjected to metal plating. Specific applications include lightweight and excellent electromagnetic shielding materials, lightweight high-capacity electrode materials for Li-ion secondary batteries and electric double layer capacitors, heat-resistant bag filters for removing dust existing in combustion gases discharged from factories etc., gas separation membranes and water separation membranes, and separators for Li-ion secondary batteries and electric double layer capacitors.
Aircrafts etc. have increasingly required heat insulation acoustic materials with a large number of voids, which have high reliability in high-temperature and low-temperature environments.
Patent Document 1 discloses a polyimide composition having a specific structure suitable for electrospinning (ESP) for bag filters to be used at a high temperature, and a method for manufacturing a non-woven fabric.
Patent Document 2 discloses that a polyimide solution is discharged from a nozzle, a fast air flow crossing the polyimide solution is applied to the polyimide solution to obtain a polyimide fiber, and the polyimide fiber is used to obtain a heat-resistant bag filter, a heat insulation acoustic material, a heat-resistant wear and so on.
Patent Document 3 discloses a separator for Li-ion secondary batteries, which is obtained using a resin solution of a polyamic acid reacted with an epoxy group-containing alkoxy silane partial condensation product.
Patent Document 4 discloses a separator obtained by applying a highly branched polymer to a porous structural material such as a non-woven fabric.
Patent Document 5 discloses a non-woven fabric composed of polyimide short fibers, which is obtained by beating a foam obtained using a polyimide having a specific structure.
Patent Document 6 discloses that when a separator obtained by laminating a porous film and a non-woven fabric is used in a Li-ion secondary battery, an electrolyte absorption rate is increased, and the separator exhibits high insulation properties.
Patent Document 7 discloses a uniform and porous electrode separator for capacitors, which is obtained using an aliphatic polyketone non-woven fabric and which is thin and tough, and has excellent thermal resistance, dimension stability, electric insulation properties, chemical resistance and low-water absorbency, the separator being suitable for production of a capacitor having a high energy density and a low internal resistance.
Patent Document 8 discloses a high-performance lipophobic polyimide membrane obtained by electrospinning a polyimide fiber with a diameter of 10 nm to 50 μm to form a non-woven fabric composed of a plurality of polyimide fibers, and treating the non-woven fabric with a perfluoro polymer.
Patent Document 9 discloses that a solution of a polyimide having a specific structure is used to obtain nano-sized fine fibers by electrospinning.
Patent Document 10 discloses that an assembly including polyimide fibers is used in a Li-ion battery separator, a bag filter or a fuel exhaust gas filter to attain both thermal resistance and solubility.
Patent Document 11 discloses that by using a polyamide-imide, a polyamide or a polyimide in a separator including a layer of organic fibers prepared by electrospinning (ESP), a decrease in capacity of a Li-ion battery can be suppressed.